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The Planet WASP-12b Is Hot As Hades And Dark As Night

October 16, 2017

Written byAshley Hamer

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The minute you think you know how things are out in space, space proves you wrong. Take WASP-12b, for instance. It's massive, hot, and super close to its home star. With all that, you'd think it would be extra bright. But it's not. It's actually pitch-black. How's that possible?

Hello Darkness, My Old Friend

How dark are we talking? WASP-12b is so dark that 94 percent of light can't escape it. Why? Its searing heat is to blame. The planet is so close to its home star that it's tidally locked, which means that one side faces the star at all times (the same way we only see one side of our moon). Its daytime side broils at 4,600 degrees Fahrenheit (2,500 degrees Celsius), which is so hot that most molecules can't even form. As a result, free hydrogen atoms in the hellish atmosphere absorb incoming light and convert it to heat.

WASP-12b was first discovered in 2008 circling a star 1,400 light years away in the constellation Auriga. This particular revelation was made by the Hubble Space Telescope, but many telescopes have studied the planet since then — not to mention its brethren. Sister planet WASP-17b, for example, is about as large, but it has the density of a styrofoam cup.

How Did They Find It?

Something that dark must be hard to find, right? Not as hard as you'd think. Instead of searching for planets in visible light, exoplanet hunters use what's known as the transit method. That technique relies on the telltale dip in brightness of a star when a planet has passed in front of it. The amount of dimming tells astronomers how large and bright the planet is. When it came to WASP-12b, astronomers didn't detect any reflected light. That's how they know that this planet is incredibly dark.

Because it's a gas giant like Jupiter but it orbits very close to its home star, WASP-12b is what's known as a "hot Jupiter." Astronomers thought they had hot Jupiters figured out until this one came along. "We did not expect to find such a dark exoplanet," said lead researcher Taylor Bell of McGill University in a press release. "Most hot Jupiters reflect about 40 percent of starlight." We're telling ya — space will fool you every time.

Wondering what else space can teach us about our world? Listen to our in-depth conversation with astronomer Michelle Nichols on the Curiosity Podcast. Stream or download the episode using the player below, or find it everywhere podcasts are found, including iTunes, Stitcher, and Gretta.